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st: RE: Detection of disease


From   "Lachenbruch, Peter" <Peter.Lachenbruch@oregonstate.edu>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Detection of disease
Date   Thu, 14 Aug 2008 08:57:08 -0700

I have my own spreadsheet I've used for many years and the sample size
calculation give n=16.  However, my question is a little different:  do
you really want to test the alternative that p=0?  This seems
unrealistic in the real world.  PASS will not accept p=0 as an
alternative.  If I use p=0.00001, it gives n=14.

I would worry about the freeware a bit.

Tony

Peter A. Lachenbruch
Department of Public Health
Oregon State University
Corvallis, OR 97330
Phone: 541-737-3832
FAX: 541-737-4001

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Carlo Georges
Sent: Thursday, August 14, 2008 2:54 AM
To: statalist@hsphsun2.harvard.edu
Subject: st: Detection of disease

I tried to reproduce in stata the calculation needed for the following
case:

I need to determine the sample size, required to detct the presence of
disease in a population.

The formula is rather complex so it is difficult to paste in here,

For example i need to detect with 95% confidence the abscence of disease
in
a population where the presumed prevalence would be 20%. How lrge a
sample
size do I need to be 95% certain that the population is free from
disease.

I used a program "Winepiscope" freeware, that calculated a samplesize of
14.

in stata i tried : sampsi 0.2 0, power(0.9) onesample

and I get a result of :16

Can stata handle this type of calculation?

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